FDA A female squid drifting more than a mile beneath the ocean surface, arms wrapped around thousands of developing eggs, has forced scientists to rethink a basic assumption about how these animals reproduce. Remotely operated vehicles operated by the Monterey Bay Aquarium Research Institute (MBARI) captured footage of the deep-sea squid Gonatus onyx holding and aerating an egg mass containing up to approximately 3,000 eggs at depths between 1,500 and 2,500 meters. The behavior, documented across multiple dives and confirmed in at least two separate squid families, contradicts the long-held view that squid simply deposit their eggs on the seafloor and swim away.
Why filmed squid brooding rewrites deep-sea reproduction assumptions
For decades, marine biologists treated squid as animals that invest nothing in their offspring after spawning. Octopuses guard their eggs, sometimes for years, but squid were assumed to follow a lay-and-leave strategy. That assumption collapsed when MBARI’s ROV Tiburon recorded Gonatus onyx females cradling egg masses in their arms, actively pumping water through tubular egg clusters to keep embryos oxygenated. The behavior was described in a peer-reviewed Nature study that established post-spawning egg care in squid, not just in octopuses or other cephalopods.
The finding matters because it changes how researchers model energy budgets, survival rates, and population dynamics for deep-sea squid species. A brooding female cannot hunt effectively while carrying her clutch. She likely starves over the course of egg development, trading her own survival for that of her offspring. Per life-history data archived at the University of South Florida, brooding females, eggs, and hatchlings of Gonatus onyx were captured at depths of 1,250 to 1,750 meters, eggs measured approximately 3 mm in diameter, and development time at cold deep-sea temperatures may reach up to approximately nine months. That timeline means a mother squid could spend the better part of a year doing nothing but protecting her offspring before dying.
The long brooding period also reframes how scientists think about risk in the deep sea. A female that carries eggs for months is exposed to predators and environmental shifts the entire time. Yet the behavior persists, which implies that the increased survival of well-developed hatchlings outweighs the cost of losing many adults. Instead of releasing clouds of tiny, vulnerable larvae, brooding squid appear to produce fewer, larger young that are better prepared for life in the dark midwater.
A testable question emerges from the data: do larger eggs correlate with even longer brooding periods at greater depths? An undescribed gonatid species observed by MBARI carried eggs of approximately 12 mm diameter, roughly twice the size seen in previous gonatid brooding observations. If egg size scales with development time, these larger eggs could demand brooding periods well beyond nine months. Cross-referencing future 4K ROV footage with temperature and depth profiles from MBARI transects could confirm or reject that relationship, and might reveal whether extremely large eggs are tied to particularly stable deep-water environments.
ROV footage and specimen data across two squid families
The evidence for squid brooding does not rest on a single species or a single dive. MBARI’s ROV Tiburon first documented Gonatus onyx females holding egg masses at depths of approximately 1,500 to 2,500 meters, with individual clutches containing up to approximately 3,000 eggs. The females were observed pumping water through the egg clusters, a deliberate ventilation behavior that keeps developing embryos supplied with oxygen in the low-oxygen deep ocean. Some females were seen with damaged arms or reduced musculature, consistent with the idea that they were nearing the end of an energetically expensive brooding period.
A separate lineage tells the same story. The deep-sea squid Bathyteuthis berryi also broods its eggs and stores sperm, according to a peer-reviewed study in the Journal of the Marine Biological Association. That two distantly related squid families share this behavior suggests brooding may be far more common in the deep sea than anyone suspected. The Smithsonian Institution’s ocean portal has historically framed squid parental care as an exception among cephalopods, but the growing list of confirmed brooders raises the question of whether the “exception” is actually widespread and simply hard to observe with traditional nets and trawls.
MBARI’s 2022 annual report added another data point. ROV Doc Ricketts filmed a Bathyteuthis species more than 90 kilometers offshore of Moss Landing, California, at 1,390 meters depth. The female was carrying approximately 360 embryos arranged in capsules within a gelatinous sheet, all captured on 4K video. Unlike the long tubular masses seen in Gonatus onyx, the Bathyteuthis clutch resembled a translucent veil, with the mother maintaining a gentle undulating posture as she ventilated the embryos.
That footage, combined with the earlier Gonatus onyx observations, gives researchers a growing visual archive of a behavior that was entirely unknown before the age of deep-diving robots. It also underscores the importance of non-destructive observation: trawl nets tend to shred delicate egg masses and separate them from adults, erasing any trace of brooding. Only slowly cruising vehicles, equipped with high-definition cameras and sensitive thrusters, can capture intact scenes of parental care in the water column.
Egg size discrepancies and gaps in the brooding record
One striking inconsistency in the data involves egg diameter. Gonatus onyx eggs, at roughly 3 mm, are small compared with the approximately 12 mm eggs documented in the undescribed gonatid species. Bathyteuthis berryi, meanwhile, carries a more modest number of embryos-around a few hundred-each enclosed in a capsule within the gelatinous sheet. These contrasts hint at a spectrum of reproductive strategies even within brooding squid.
In general, larger eggs tend to produce larger, more developed hatchlings that can swim and feed on their own immediately. Smaller eggs usually yield larvae that must pass through additional developmental stages in the plankton. If deep-sea brooding squid are investing in larger eggs, they may be skipping vulnerable planktonic phases altogether, releasing juveniles that can immediately take advantage of patchy midwater food sources.
However, the record is patchy. Most of what scientists know about deep-sea cephalopods comes from specimens hauled up in nets, often damaged and separated from any eggs they might have been carrying. ROV sightings remain rare events, and brooding females may be especially difficult to find if they occupy specific depth bands or avoid bright lights. That means current estimates of egg size ranges, clutch sizes, and brooding durations are still based on a handful of encounters.
There is also a methodological complication: magnification and lighting can distort apparent egg size in video, particularly when translucent capsules overlap. Without physical samples, researchers must carefully calibrate image scales and compare them with environmental reference points in the frame. As more dives incorporate laser scaling systems and paired sampling, scientists hope to reconcile discrepancies between video-based measurements and net-collected specimens.
Another gap lies in the earliest and latest stages of brooding. Many filmed females are already carrying well-developed embryos, with visible eyes and chromatophores. Far fewer observations capture the initial moment when eggs are first extruded and arranged, or the final phase when hatchlings emerge and the mother dies. Those bookend stages could reveal whether females adjust their depth, swimming behavior, or even bioluminescent signaling as the clutch matures.
What deep-sea brooding reveals about life in the abyss
Viewed together, the emerging data on Gonatus onyx, Bathyteuthis berryi, and related species point to a broader reappraisal of deep-sea life histories. Rather than relying solely on high fecundity and low parental investment, at least some squid appear to be following a strategy more often associated with birds or mammals: fewer offspring, more care.
This shift has cascading implications. Population models that assume every adult can spawn multiple times may need revision if brooding is a one-time, terminal event. Estimates of growth rates and resilience to fishing pressure could change as well. If a significant fraction of deep-sea squid species brood their eggs, they may be more vulnerable to disturbance than previously thought.
Brooding also highlights how little is known about basic behaviors in the deep ocean. The same ROVs that revealed egg-carrying squid have documented other unexpected scenes, from gelatinous predators hunting with sticky tentacles to fish drifting upside down in supercooled water. In each case, direct observation has overturned textbook assumptions built on fragmentary specimens.
As more high-resolution cameras descend into the midwater, scientists expect to find additional brooding species-and perhaps even more elaborate forms of parental care. For now, the image of a solitary squid hovering in the dark, cradling a shimmering mass of eggs for months on end, stands as a reminder that even in the planet’s most remote habitats, evolution has repeatedly found ways to make parenting pay off.
Researchers continue to refine these insights using new analytical tools, including improved access systems such as the Springer Nature platform, which help synthesize scattered reports into a more coherent picture of deep-sea reproduction. Each new observation adds another piece to the puzzle, suggesting that the abyss is not simply a realm of anonymous drifting larvae, but a place where devoted parents quietly guard the next generation in the dark.
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*This article was researched with the help of AI, with human editors creating the final content.
